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Hair has been credited with being a man's strength, a woman's allure, and the savior of modesty. But even if you're not Samson, Rapunzel, or Lady Godiva, the mythology of hair also has applications for those of us living in the stressful reality of modern life.

It has been said that stress can make you go gray, or cause you to lose your hair. Is that possible?

Sometimes, you might feel like tearing your hair out due to personal, economic, and work-related stresses, but stress won't likely be the direct cause of gray hair. A 2009 study in the journal Cell found that unavoidable damage to the DNA in cells that produce the pigment responsible for hair color is most likely the culprit that causes a hair to turn white.

But can stress accelerate the aging process on a cellular level and, as a result, cause you to go gray before your time? Right now, the answer is debatable.

"We have all witnessed the graying hair of many past presidents. Perhaps over long periods of stress, there may be an acceleration of gray hair in some people," says Amy McMichael, MD, professor of dermatology at Wake Forest Baptist Health in Winston-Salem, N.C. But, she points out, that idea is mainly speculation. "I don't know of any studies showing this," she says, "and I'm not sure I have a scientific answer."

If the jury's still out on the question of stress being responsible for turning hair gray, then what's the verdict on stress and hair loss? Is there a relationship?

Paradi Mirmirani, MD, a dermatologist with the Permanente Medical Group in Vallejo, Calif., says it all depends on what type of stress you're talking about. "Stress because you're late to work or you've got a heavy workload is not going to cause you to lose hair," she says. Mirmirani, a member of the North American Hair Research Society, tells WebMD that short-term, everyday stress is not going to affect your body in such a way that your hair falls out. It takes something larger to do that. "Something that causes you to lose sleep," she says, "or changes your appetite and raises the level of stress hormones."

McMichael puts it more bluntly. "There has been, for my entire life, this mythical connection between stress and hair. It's absolutely ridiculous." McMichael says there is no evidence to support the idea that just because you had a few stressful days last week, your hair will fall out this week. "It doesn't even work that way," she says.

Stress and Hair: The Hair Cycle

A normal head of hair contains about 120,000-150,000 strands of hair. Usually, at any one time, about 90% of those hairs are in a growing phase, growing by about 1/2 inch each month. This phase lasts for two to three years. At that point, a hair will go into a resting stage. This "rest" lasts for 3 to 4 months before the hair falls out and is replaced by a new one.

Sometimes, a significant stress of some sort may spark a change in your body's routine physiological functions, Jacobs says, and cause a disproportionate number of hairs to go into the resting phase at the same time. Then three to four months later, sometimes longer, all those resting hairs are shed. The effect can be alarming. The types of events that disrupt the normal hair cycle, Jacob tells WebMD, can be caused by the substantial physiological stresses on your body.

But, according to McMichael, physiological stress is not the same as emotional stress. Hair loss can be one way the body responds to significant physiological stress that may be brought on by diet, medical, or lifestyle changes.

"Only those things that cause physiological stress can cause a hair loss event," McMichael says. The good news is that the hair loss from these kinds of events is usually only temporary, as long as the stress event is temporary. Once the stressor is addressed, or goes away on its own, hair grows back and the normal hair cycle resumes.

Stress and Hair: What Causes Hair Loss?

A variety of stressors may cause your body to undergo hair loss. It happens, McMichael says, when there's some type of physiological change in your system. "For instance," she says, "you go on or off an oral contraceptive. Or you lose more than 15 pounds of weight. Things like this change the physiological balance in your system."

Other stressors, according to McMichael, could include:

Being on a strict low-calorie diet

After childbirth when estrogen levels fall

Severe illness

Having a high fever

Having major surgery

Severe infections

Mirmirani says that hair shedding can also result from certain medications such as some type of blood pressure medications, thyroid disease, and nutritional deficiencies such as vitamin D or excess vitamin A.

Pinpointing the actual cause of the shedding isn't always easy. That's because, Mirmirani says, there's a three- to six-month lag time between the stressful event and the hair loss. In order to determine the cause, you need to look back at what was happening three, six, or even nine months before the hair loss began.

Stress and Hair: The Physiological & Emotional Connection

"If you're going through a very severe divorce," McMichael says, "you might not be eating properly; you might lose weight or not sleep well. You may go off and then back on your oral contraceptives." All of these things cause physiological stress and an imbalance in your system. "The point is," she says, "there are a lot of other things that are physiological going on. You're not losing your hair because you hate your ex-husband."

McMichael says that women have a number of things that happen on a regular basis that they may not recognize as stressors. "You start out your life and you're fine," she says. "You're 20 years old and get married. You get on some oral contraceptives. Well, that causes shedding."

When a woman decides to have a baby, if she is taking them, she will stop taking oral contraceptives. "Maybe you have a little bit of shedding related to that. And then you get pregnant." Pregnancy causes the body to keep the hair that normally would fall out as part of the regular hair cycle, so a woman may notice her hair may feel extra thick and fuller during that time. After giving birth, all the hair that would have fallen out is shed three to six months later.

"Also, after birth," McMichael says, "you realize you've gained 30 pounds and go on a diet to lose it. That causes shedding. But somewhere in all this, someone in the family dies and, because you've heard that stress causes hair loss, you say, 'Oh my God, I'm losing my hair because someone died.' But that's not it. You're losing hair because you lost 30 pounds."

"It's not a foregone conclusion," McMichael says. "Not everyone gets these episodes of hair loss. Some women go on and off of contraceptives and never have shedding. Some have seven children and have no hair loss related to it." McMichael does point out that once you have shed hair in response to a physiological stress, you are likely to do it again.

McMichael says that because people have repeated the myth of a direct connection between emotional stress and hair loss for so many years, many people now believe it. Jacob tells WebMD. "There's no way to predict who's going to lose hair and who's not. If you're a shedder, you'll shed." She also says there's no scientific evidence that points to specific emotional stresses that might trigger the physical stress that can lead to hair loss.

Seeing a Doctor About Hair Loss

Unlike other types of hair loss that are more often permanent, hair loss during the normal hair growth cycle happens suddenly. It also doesn't normally cause bald spots, or follow a pattern like genetic or autoimmune-related hair loss. Instead, it's diffuse and causes thinning of the hair across the scalp. That’s because each of the 120,000-150,000 hair follicles is independent of other hair follicles, and is in its own cycle of growth -- some are growing while others fall out.

You may notice after washing your hair that handfuls of hair have fallen out. "But," says Mirmirani, "usually by the time someone notices the shedding, the hair is already growing back. Whatever caused it happened three months or more before. The new hair growing in is pushing the resting hair out."

That doesn't mean there's no reason to go to the doctor. Hair loss can be an early sign of about 30 different diseases. "It's never too early to talk to a doctor about hair loss," Jacob says. "The doctor can evaluate what's happening and help you understand it and know what to do." She says that products on the market, such as over-the-counter minoxidil and various supplements that are sold for hair loss, can actually cause problems if they're not truly needed and not used properly. It's important, she says, to discuss the use with the doctor first.

McMichael says a doctor can also help you identify the particular stressor that's causing the shedding. "There may be lots of things going on that's causing it. A doctor can help you find them out and help you know how to address them." Once the causes of stress are addressed, the shedding should stop and your hair should return to normal.